c++定义学生类，有私有成员

定义学生类，有私有成绩属性score, 有公有函数show用来输出成绩，添加-一个静态数据成员totalscore， 用来计算所有学生的总成绩，再添加-一个公有静态函数成员Alll用来显示totalscore的值，要求类中要有构造函数、拷贝构造函数，析构函数，在主函数中定义不少于三个对象进行测试。

#include <iostream>
using namespace std;

class Student
{
private:
    int score;
    static int totalscore;

public:
    Student(int s) : score(s) { totalscore += s; }
    Student(const Student &s)
    {
        score = s.score;
        totalscore += score;
    }
    ~Student() { totalscore -= this->score; }
    void show() { cout << "score: " << score << endl; }
    static void ALL() { cout << "total score: " << totalscore << endl; }
};

int Student::totalscore = 0;

int main()
{
    Student s1(50);
    s1.show();
    Student::ALL();
    // score: 50
    // total score: 50

    Student s2(60);
    s2.show();
    Student::ALL();
    // score: 60
    // total score: 110

    {
        // 赋值构造测试
        Student s3(s1);
        s3.show();
        Student::ALL();
        // score: 50
        // total score: 160
    } // 析构s3;
    Student::ALL();
    // total score: 110
}